Microscopic-scale Defect Identification in β-Ga₂O₃ Epitaxy

β-gallium oxide (β-Ga₂O₃) is a promising ultrawide bandgap semiconductor for next generation high power electronics that can surpass the performance of silicon, silicon carbide, and gallium nitride. In addition, the facile growth of crystalline β-Ga₂O₃ has significantly contributed to the rapid development of β-Ga₂O₃ power devices. However, device performance issues remain, where crystalline and thin-film defects contribute to this limiting factor. Crystalline defects in technologically mature materials have been identified and classified,^{1, 2} since it is economically beneficial to isolate failure mechanisms at the source rather than relying on backend testing after device fabrication. The various defects could be categorized into killer or non-killer defects, where killer defects can hinder the operation of high-performance devices by trapping charge carriers or causing increased leakage current. The defects in Ga₂O₃ are largely unclassified, therefore identifying defects that cause electrical device degradation must be solved for widespread adoption of β-Ga₂O₃.<br><br><br/>In this work, photoemission electron microscopy (PEEM) is used to visualize micrometer-scale defects and determine their electronic impact. PEEM is based on the photoelectric effect and is a non-destructive analysis method where light is used to excite and eject electrons from the sample surface and these electrons are analyzed. We investigated the defects on commercially-available epitaxially-grown β-Ga₂O₃on (010) β-Ga₂O₃ substrates. The epitaxy was formed by hydride vapor phase epitaxy (HVPE) with a target doping of 1 10¹⁸ cm^-3 on the (010) semi-insulating β-Ga₂O₃ wafer. We identified two types of elongated structures on the β-Ga₂O₃ epi-layer that appear in multiple locations on the sample surface and are oriented in a parallel direction. One of these features resembles the “carrot” defect observed in SiC epitaxy.³ The carrot defect appears topographically as a bump with a density of 5 x 10⁴ cm^-2, and shows a difference in the electronic properties (either in work function and/or gap states) compared to the non-defect surroundings. The second defect, or line defect, appears as depression with a higher density of 2 x 10⁵ cm^-2 and shows no change in electronic properties compared to non-defect surroundings. The local electrical influence of these defects are investigated with tunneling atomic force microscopy (TUNA), and both defects display reduced current compared to the non-defect surroundings. Ongoing work to identify the structural origin these defects through transmission electron microscopy will be presented. Together, we will present a discussion on the nature of these distinct features and their implication on device performance.<br><br/>References<br/>1. H. Das, S. Sunkari and H. Naas, ECS Transactions <b>80</b> (7), 239 (2017).<br/>2. P.-C. Chen, W.-C. Miao, T. Ahmed, Y.-Y. Pan, C.-L. Lin, S.-C. Chen, H.-C. Kuo, B.-Y. Tsui and D.-H. Lien, Nanoscale Research Letters <b>17</b> (1), 30 (2022).<br/>3. M. Benamara, X. Zhang, M. Skowronski, P. Ruterana, G. Nouet, J. J. Sumakeris, M. J. Paisley and M. J. O’Loughlin, Applied Physics Letters <b>86</b> (2) (2005).